The present invention relates to phased array antennas, and more particularly, to a semi-active phased array antenna.
The two basic types of phased array antennas are the active phased array antenna and the passive phased array antenna. A passive phased array antenna has a single, centralized transmitter and receiver connected to the feed line to the antenna. The active phased array antenna provides a separate high power amplifier and a low-noise receiver amplifier at each radiating element.
Currently, the cost of a passive phased array antenna is an order of magnitude lower than that of an active phased array antenna. For example, the cost of a phase shifter module in a passive phased array antenna is approximately $200 compared to $8,000 for an active transmit and receive module in an active phased array antenna. The disadvantage of the passive phased array antenna is the additional ohmic loss between the transmitter/receiver and the radiating aperture due to the beam forming feed and phase shifters. The disadvantage of the active phased array antenna is the high cost of the solid state high-power amplifiers in the active modules.
Accordingly, it is a feature of the present invention to provide a semi-active phased array antenna which provides high power in transmit mode and a low noise figure in receive mode.